I'm due to have an Octopus solar installation next week. This includes two GivEnergy products: a GivBat 9.5 and a GIV-HY3.6 Hybrid Inverter. The solar panels are JAM54D41 LB - there will be 11/13 of these.
Also Octopus are installing an air source heat pump in July. I see that there is a higher spec inverter. Would I be wise to see if they can change this?
Thanks.
Depends on the peak output of the panels.
You want that to more or less match the inverter specs, or slightly less than the panels (clipping on a very sunny summer day Vs better generation the rest of the time).
If the inverter is too big for the panels, the startup voltage required might mean generation is missed - e.g. it needs to be sunnier than it really needed to be.
So if the inverter is 3.6 kW model and the panels are 4kWp that might be about right (with some clipping).
But if the inverter was the 5kW model and the panels were 4kWp not ideal for efficiency and startup voltages.
npj If that's a Gen1 inverter then don't accept it, they're end-of-life.
Also I'd go for a 5kW inverter as the 3.6kW inverters are limited to 2.6kW charge/discharge on the battery (depending on gen). 5kW will allow 3.6kW charge/discharge from battery.
And get as many panels as you can fit on the roof! Whilst you have the cost of scaffolding and the installers on site, it's best to maximise the investment!
npj Looks like JAM54D41 ranges from 430W to 455W, so that could be from 4730W to 5915W.
I got Solar from Octopus about 6 months ago, and they upgraded me to a gen-3 hybrid (5kW, but I have slightly more panels).
According to https://wiki.terravolt.co.uk/docs/inverters/ the gen-2 3.6kWh inverter has 3.6kW to/from the battery. (And so would the gen-3, I expect.)
Bear in mind that upgrading to 5kW inverter will require a G99 (?) certificate in advance, so you'll probably have to slip the date, depending on the region/DNO. (SSE are spectacularly slow at processing these applications.) Whereas 3.6kW inverter requires a G98 which is done after the install.
A heat pump will of course wants lots of energy. But assuming most of that's coming from the battery, rather than the sun, then the battery interface is the limiting factor, and that's 3.6kW for both 3.6kW and 5kW inverters. The only thing the bigger inverter gives you is being able to generate AC from both solar and battery at the same time.
A couple of thoughts on the current, Gen3 inverters:-
The 3.6 and 5kW inverters have identical solar voltage/MPPT ranges. They also have identical maximum battery charge and discharge powers. The 5kW, however can output more AC on a sunny day with or without the aid of the battery/ies.
The 5kW can be run happily on a G98 approval, it'll just get limited to 3.6kW export at installation time.
The wholesale price of both inverters is almost identical at the moment
Many thanks for all your speedy replies - they are much appreciated.
As the scaffolding has been put up this morning, ready for installation on Monday, I'll have no time to apply for certificates so I'll go with what I have.
The installers are bringing extra panels to maximise the roof coverage.
As you can tell I'm a novice in this area and I hope you don't mind a subsidiary question or pointing me to the best area to post a message...if there is a power cut I understand that the battery will not be charged up as a safety precaution (but I can use the stored energy); is there some isolator switch to allow me to continue charging whilst the power cut continues?
mrand31
Thanks. I'll ask Octopus if it is possible.
npj if there is a power cut I understand that the battery will not be charged up as a safety precaution (but I can use the stored energy); is there some isolator switch to allow me to continue charging whilst the power cut continues?
I think you may have misunderstood... if there's a powercut, the inverter will isolate itself from the AC side for safety, so it won't power your house. But the DC side can continue working, so it can keep charging the battery from solar.
The inverter can be configured to power the house during a power cut. Requires some changes to the house wiring to achieve (depending on the level of cover required). Octopus told me that they won't do it themselves, but are happy for someone else to do it. But I'm not sure how that affects warranties and things - if someone else was the last to touch the inverter, I can imagine Octopus may not want to continue as responsible party. (I need to follow this up at some point.)
mrand31 The 5kW can be run happily on a G98 approval, it'll just get limited to 3.6kW export at installation time.
My install was held up for ages waiting for the G99. I did enquire whether the 5kW could be software-restricted to 3.6kW initially, then released later, but that apparently not. Problem is that they'd have to do the G98 for the install, and that would complicate the ongoing G99 application. Or something... There's also some sort of fast-track for G99 under certain circumstances, but they didn't want to try it that way either.
DD
Thanks for the helpful reply, I'd not understood that. I'll hope to sort something out for the future.
With our system there was a change of system just prior to installation and we still had the system put in on the planned date. The system was generating whilst the new G99 was being processed. However we were not paid for any excess being exported as OE would not change us over to the flux tariff until the G99 was granted.
DD Looks like JAM54D41 ranges from 430W to 455W, so that could be from 4730W to 5915W.
So G99 territory then. Must be a split array or why would anyone sane install a 3.6kW inverter?
Vestas That seems slightly harsh. Even the 3.6 can accept 7.5kW on the input. Just need to be a little careful in making sure you have space in the battery so that you can utilise both 3.6kW output channels (AC and battery) concurrently.
(That's related to the game I'm currently playing: I want to export solar directly, without charging the battery, but since solar can exceed 5kW, I need to be able to redirect a little to the battery to avoid clipping. So I want to build a modbus-based monitor which keeps an eye on the AC output, and tweaks the charging rate to ensure the battery is consuming just enough. But these pesky clouds don't half make it hard !)
DD (That's related to the game I'm currently playing: I want to export solar directly, without charging the battery, but since solar can exceed 5kW, I need to be able to redirect a little to the battery to avoid clipping. So I want to build a modbus-based monitor which keeps an eye on the AC output, and tweaks the charging rate to ensure the battery is consuming just enough. But these pesky clouds don't half make it hard !)
Have a look at this python based solution for Home Assistant that identifies clipping and recommends (not yet changing) charging rates https://github.com/springfall2008/batpred/issues/886
geoffreycoan Doh! Thanks, yes, I had seen that, but then promptly forgot about it.
I didn't really see the need to involve solar forecasting - I reckoned it was enough to just poll the AC generation register directly through modbus, and try to keep it below about 4800. That's easy enough. The interesting challenge is deciding when it's safe to reduce the charging rate - I don't want to have it reduce too quickly, nor adjust it every few seconds, but I also don't want to have it spend long periods charging too much.
Currently playing with moving averages, and detecting crossings of fast MA over slow MA, and things like that. (The sort of tricks for trying to predict share movement. But solar is very volatile.)
DD You have been misinformed. I have a 5kW inverter and it was installed under G98 by mistake. Either the installer or GivEnergy tech support can restrict the export to a max or 3.6kW until you get the G99 sorted retrospectively. This was what happened to my system so it can be done - it's just not visible on the portal or adjustable by an end user. Some DNOs seem to allow fast track G99 approvals and the installer must perform and submit various Earth loop Impedance measurements to send with the application. I think this is to ensure that your local grid segment can accept 5kW.